Contributing an 8080 demo to emuStudio

Encouraged by the emuStudio developer, I donated to the project an Intel 8080 Assembly demo. It's a modified version of Twirl, my program to display a twirling bar animation.

Here's the code I contributed:

; Twirling bar animation by Paolo Amoroso <>
; Runs on an Altair 8800 with an ADM-3A terminal. Press any key
; to interrupt the program.

FRAMES    equ  8              ; Number of animation frames

CLS       equ  1ah            ; ADM-3A escape sequence
HOME      equ  1eh            ; ADM-3A escape sequence
STATUS    equ  10h            ; Input status port
READY     equ  1              ; Character ready status mask

          mvi  a, CLS         ; Clear screen
          call putchar

loop:     lxi  h, ANIM        ; Initialize frame pointer...
          mvi  b, FRAMES      ; ...and count

loop1:    mvi  a, HOME        ; Go to home
          call putchar

          mov  a, m           ; Print current frame
          call putchar

          push psw
          in   STATUS
          ani  READY          ; Key pressed?
          jnz  exit           ; Yes
          pop  psw

          inx  h
          dcr  b
          jnz  loop1

          jmp  loop

exit:     pop psw             ; Clear psw left on stack

ANIM:     db   '|/-\|/-\'     ; 8 frames

include	'include\'

Unlike the original code, which I designed to run on emuStudio and be easy to port to CP/M, this new version is intended to run only on emuStudio. This was an occasion to simplify the code.

The main difference is the escape codes for VT100-compatible terminals on CP/M are strings, whereas the ADM-3A codes Twirl sends on emuStudio are single bytes. This allows the program to print the codes with the putchar library subroutine instead of putstr. Doing away with putstr no longer requires saving and restoring the HL register pair in the calling sequences.

Finally, I added code to terminate the program if a key is pressed.

#intel8080 #Assembly

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